In electrical engineering, the collective term coil winding technology is understood to mean any manner and method of winding up electrical conductors into a coil. In this case, “coils” should not be understood just to be separate inductive passive components; rather, in the present connection, the term covers all windings and winding materials which are suitable for generating or detecting a magnetic field. The windings of actuators, in particular of the stator and rotor of a rotating electric machine, are likewise denoted coils in the following text within this further meaning.
Winding technology thus essentially determines the properties of electromechanical assemblies having windings. These include the dielectric strength, the quality factor, the size required for a particular power or magnetic force, or the magnetic stray field. Because the requirements for energy efficiency are increasing greatly in the prior art, there are, in particular, increasing demands for the development of components for electromechanical assemblies such as electric motors.
Windings in stators and/or in rotors are usually wound especially with comparatively thin single wires—typically ones with a diameter of up to 2 mm—which are introduced into the openings (slots) in the stator or rotor iron manually or using corresponding winding and drawing-in machines. It is a known procedure to introduce bars rather than single wires into the slots, to shape these single bars and subsequently to connect, for example weld, them at their ends to form a continuous winding. Since especially short U- or V-shaped single segments that are reminiscent of hairpins are used for this purpose in the prior art, such bar windings are sometimes referred to as hairpin conductors among those skilled in the art.
Bar windings afford various advantages compared with single-wire windings: While single-wire windings still require various manual steps during manufacturing, in spite of the high degree of automation, bar windings can be produced completely automatically. In this case, the bars usually have a rectangular cross section and are segmented into equal cross sections in the slot. Bar windings thus allow better exploitation of the slots than single wires, which leave empty spaces even when tightly packed and cause a substantial loss of space as a result of insulation coating. As a result of the greater filling of the slots with copper (known as the copper filling factor), greater machine capacities can be achieved with less installation space. While, in the case of single wires, filling factors of 30% to 50% are conventional, with bar windings it is even possible to achieve more than 80%. As a result of the well-defined surface and the greater dimensions of the hairpin or bar conductors, more reliable insulation is possible both between the bars and between bars and iron. The deterioration of the insulation is one of the most significant aging mechanisms and central for the lifetime of electric machines. In the case of U-shaped segments, the single segments can be inserted into the slots from the end side during manufacturing, with the result that slots that are closed toward the air gap and are half-open are realizable, this being difficult or even impossible with single-wire windings with a continuous wire, as explained in U.S. Pat. No. 8,330,318, which is incorporated by reference herein. If the electric machine is operated at high speeds with a bar winding, the losses of the electric machine increase on account of high-frequency effects.
JP 2011 147 312 A, which is incorporated by reference herein, describes a stator winding of an electric machine, wherein various winding cross sections are provided within the slots. In that case, the windings with a smaller cross section are preferably located further in than the windings with a larger cross section.
US 2004 0207 284 A1, which is incorporated by reference herein, describes an electric machine having a stator winding made up of radially arranged conductor segments with a rectangular cross section.
US 2012 0025 660 A1, which is incorporated by reference herein, describes an electric machine having a stator winding with a multiplicity of windings with a rectangular cross section. Each winding in that case consists of two portions, wherein the inner portion of a winding is connected to an outer portion of a winding in a non-adjacent slot.
US 2012 0274 172 A1, which is incorporated by reference herein, describes an electric machine having a stator winding made up of a multiplicity of line bundles, wherein the cross section of the line bundles is flexible. The line bundles in that case are arranged such that they come into contact with adjacent line bundles.
US 2015 0311 757 A1, which is incorporated by reference herein, describes an electric machine having a stator winding made up of a multiplicity of coil conductors. In that case, the coil conductors can have different, in particular also curved cross sections.
US 2016 0013 692 A1, which is incorporated by reference herein, describes a stator for an electric machine having a multiplicity of windings which are arranged radially and the cross section of which changes depending on their position.
U.S. Pat. No. 5,801,471 A, which is incorporated by reference herein, and U.S. Pat. No. 6,252,327 B1, which is incorporated by reference herein, show further prior art relating to stator windings for electric machines.
As soon as a plurality of different conductor bar forms are required for an electric machine, it is often not advantageous to acquire them from a manufacturer on account of the now smaller quantity of each conductor form. Instead, production in situ from a single raw material inline during the manufacturing process of the machine would be desirable.
In principle, such dynamic rolling is known from the prior art. For example, EP 1 074 317 A2, which is incorporated by reference herein, describes and illustrates a method for the flexible rolling of a metal strip, wherein, during the rolling process, the metal strip is guided through a rolling gap formed between two work rolls and the rolling gap is moved in a deliberate manner during the rolling operation in order to achieve different strip thicknesses along the length of the metal strip. As a result, good flatness of the metal strip is intended to be achieved, even in the case of relatively wide strips, specifically in that, during each operation of setting the rolling gap or immediately thereafter, the elastic lines of the work rolls are controlled depending on the rolling gap set in order to achieve flatness of the metal strip.
However, such methods are provided almost exclusively for the rolling of metal strips. Curves and irregular material thicknesses along the strip are usually undesired. Only a systematic regional material weakening by way of deliberately thinner portions is proposed occasionally in the specialist literature for producing components in a material-saving manner.